Earlier quoted context omitted.
This seems to just be a result Apple's poor OpenGL stack. Krita has been very stable on both Linux and Windows for me. From their roadmap page: "We will spend more time on macOS. Even though Apple’s support for the technologies Krita needs, like OpenGL, sucks."
Any hope for support of things like Metal at all maybe?
And Krita shouldn't be more unstable on macOS than on Windows or Linux, but it doesn't get tested as well, and there are so few macOS developers who want to take a hand. Personally, I develop on Linux but use Krita on Windows, when I find time to work on my own comic. The macbook pro only gets opened to make builds or fix the occasional macOS-specific bug.